The invention relates to a bumper system for a motor vehicle.
The primary purpose of bumper systems is to absorb the impact when a motor vehicle strikes an obstacle, and to protect the vehicle body from structural damage during a low-speed collision. Bumper systems also protect pedestrians when they come into contact with a motor vehicle.
Current bumper systems generally comprise a flexurally rigid cross-member that is arranged horizontally and perpendicular to the direction of travel, and is coupled to each of two longitudinal supports on the vehicle body via components known as crush boxes. In a low-speed head-on collision, the type of collision that is typical in city driving, the crush boxes absorb the impact energy with plastic deformation. Statutory provisions imposed on and negotiated agreements accepted by the automobile industry with regard to protecting pedestrians provide that bumper systems should also minimize the stress on the lower extremities of pedestrians if there is contact between a pedestrian and the front of the vehicle. To this end, impact tests with a leg impacter are among the various tests performed on bumper systems that must meet compliance within a number of limits or parameters.
With respect to pedestrian protection, in the most common bumper system, at least one energy absorption element is attached directly to the front of the cross-member.
DE 44 13 641 C1 describes a bumper system in which impact absorption elements made of energy-absorbing plastic foam or a plastic honeycomb structure are arranged on the front of the cross-member.
Resilient structures are also attached to the front of the cross-member, in addition to plastic foams, plastic honeycomb structures, and porous energy absorption elements. DE 32 32 940 C2 discloses an energy absorption element configured as an undulating leaf spring. Moreover, thin strips of sheet that are attached to the cross-member as open profiles are used for the energy absorption element.
DE 198 06 541 A1 describes a cross-member that is configured as a shell and on which plastic foam layers having different densities are provided. The shell configured in this manner is attached to a flexurally rigid cross-member, and when the plastic is compressed in an impact, it can press backward, thus at least partially absorbing the impact energy.
In addition to passive systems, bumper systems are known which react to an impact with actively controllable elements. Thus, DE 198 47 385 C1 describes a system in which the bumper can be actively moved between a rest position and a functional position. The movement is accomplished using spring elements or elements made of a shape memory material.
DE 10 2007 012 962 A1 describes an actively switchable lock between a crush box and a cross-member. If there is contact with a pedestrian, it permits a bumper, including the crush box, to be pushed into the cross-member with low resistance.
JP 04 154 457 A discloses a bumper system for a motor vehicle, which has a cross-member that is arranged essentially transverse to the longitudinal supports of the vehicle frame. It also has crush boxes that are incorporated between the cross-member and the longitudinal supports. The cross-member may also be moved out of a ready position towards the longitudinal supports. Specifically, it can be moved both horizontally and vertically relative to the crush boxes. When displaced in this manner, the cross-member is pressed obliquely downward, and the energy absorption element in the form of connecting bars between the cross-member and the crush boxes, is deformed. Moreover, an energy absorption element made of a foamed material is provided between the cross-member and the front cover.